A finite difference time domain (FDTD) method is one method of analyzing transitional behavior of an electromagnetic field by a numerical simulation using a computer. Further, there is a method of analyzing transitional behavior of a circuit by a numerical simulation through the execution of a circuit analysis program, such as simulation program with integrated circuit emphasis (SPICE), by a computer.
There are numerical simulation methods that integrate electromagnetic field analysis and circuit analysis (hereinafter, “integrated simulation method”). An integrated simulation method can collectively analyze the characteristics of circuit elements and surrounding electromagnetic field phenomena and therefore, is very useful for analyzing high-frequency signals propagated in the circuit.
Herein, the applicant presents a proposal concerning a simulating apparatus that executes an integrated simulation method such as that disclosed in Japanese Laid-Open Patent Publication No. H11-153634. In the proposal, the link between electromagnetic field analysis and circuit analysis is facilitated by respectively correlating an electric field and a magnetic field of a cell that is allocated with external terminals of a circuit for the FDTD method (hereinafter, “circuit cell”) with a voltage and a current of an equivalent circuit connected to the circuit terminals. According to the proposal, a stable solution can be obtained with a small amount of calculation.
However, when a conventional integrated simulation method is executed using one computer having a single central processing unit (CPU), the area to be analyzed is restricted by calculation resources such as the capacities of the hard disk and memory. The time necessary for the calculation is substantially determined by operating speeds of the CPU and the memory.
Therefore, to analyze a larger area at a high speed, parallel processing by multiple CPUs is desirable. Thus, with respect a large area for which analysis is difficult by one computer, a system that efficiently executes analysis in a short time by parallel processing using multiple computers and without a decrease in the precision of the analysis by a conventional integrated simulation method has been proposed (see, for example, Japanese Laid-Open Patent Publication No. 2004-54642).
A computer or a CPU of such a system is referred to as “processing apparatus” hereinafter. To avoid confusion in the description hereinafter, physically different components having the same name will be distinguished from each other by a single letter or consecutive letters (such as “A” or “Aa”) appended to the name.
FIG. 11 is a diagram of a configuration of an area that is to be analyzed and is divided according to a conventional integrated simulation method employing parallel processing. As depicted in FIG. 11, a printed circuit board 1 is divided, by a dividing border 2, into electromagnetic field analysis areas H3 and J4. Circuit units F5 and G6 are respectively disposed in closed spaces of the electromagnetic field analysis areas H3 and J4. The circuit units F5 and G6 each include circuit elements such as an LSI.
FIG. 12 is a diagram of a configuration of a conventional simulation system that executes an integrated simulation method employing parallel processing. In the analysis of an area having a configuration as depicted in FIG. 11, as depicted in FIG. 12, processing apparatuses A11, B12, D13 and E14 respectively are responsible for electromagnetic field analysis executed with respect to the electromagnetic field analysis areas H3 and J4, and for circuit analysis executed with respect to circuit units F5 and G6.
Magnetic field data (H) and electric field data (E) are transmitted and received between the processing apparatus A11 and B12. Capacity data (C), current data (I), and voltage data (V) are transmitted and received between the processing apparatuses A11 and D13 and also between the processing apparatuses B12 and E14. On the other hand, no data is transmitted or received between the processing apparatuses D13 and E14. This is because, as depicted in FIG. 11, the circuit units F5 and G6 are respectively disposed in closed spaces of the electromagnetic field analysis areas H3 and J4.
FIG. 13 is a diagram of a configuration of an equivalent circuit of a circuit unit employing a current source method. As depicted in FIG. 13, an equivalent circuit 21 is represented by a current source 23 connected between both terminals of a circuit model unit 22, and a capacitor 24 connected in parallel to the current source 23. Based on the equivalent circuit 21, circuit analyzing units Da15 and Ea16 respectively of the processing apparatuses D13 and E14 each execute, for example, circuit analysis by the SPICE and obtain a voltage V applied between both terminals of the circuit model unit 22.
However, in the above conventional integrated simulation method employing parallel processing, if the circuit unit spans multiple electromagnetic field analysis areas due to the division of the space, when circuit analysis of the circuit unit is executed for a portion included in one electromagnetic field analysis area, data on the current and the voltage of another portion included in another electromagnetic field analysis area is insufficient. Therefore, no circuit analysis can be executed.
Thus, as a preventative measure, as depicted in FIG. 11, the printed circuit board is divided such that each circuit unit is disposed in a closed electromagnetic field analysis area. However, on an actual printed circuit board, many circuit parts are disposed complicatedly entangled with each other. Therefore, to divide a printed circuit board in such a manner is quite difficult. That is, when many LSIs are mounted on a printed circuit board as is recently the case, a problem arises in that simulation cannot be executed.